Separating apparatus for flat pieces of different dimensions

ABSTRACT

Apparatus for separating pieces of sheet-like material having different marginal dimensions from each other. The pieces travel over means for sensing the lengths and or widths thereof, and the pieces having certain lengths and/or widths are directed to a suction conveyor which conveys them over an opening in the apparatus, while pieces having less than said lengths and/or widths are allowed to drop through said opening.

I United States Patent 11 1 1111 3,918,586

Tyler et al. Nov. 11, 1975 SEPARATING APPARATUS FOR FLAT 3,395,9158/1968 Clausen et a1. 271/197 PIECES OF DIFFERENT DIMENSIONS 3.476.24111/1969 Ungerer 209/74 R X 3,621,266 11/1971 Akuta 250/560 1 lnvemorsiRegmald Tyler, New 3.727.911 4/1973 Vits 271/195 Westminster; Paul M.Carter, Vancouver, both of Canada n N K 1 Prinmry E.1'anzinerA en now es[73] Assrgnee: Durand Machine Comp y Attorney, Agent, orFirm-Fetherstonhaugh & Co.

New Westmmster, Canada [22] Filed: Dec. 27, 1973 [21] Appl. No; 428,866[57] ABSTRACT Apparatus for separating pieces of sheet-like material[52] 209/74 R3 209/1 11-7; 271/197 having different marginal dimensionsfrom each other. [51] Int. Cl.- 8651'! 7/16 The pieces travel over meansfor Sensing the lengths [58] Fleld 0f Search 209/73, 74, 111.7; and orwidths thereof and the pieces having Certain 271/1971 1941 1081250660;lengths and/or widths are directed to a suction con- 356/157 158 veyorwhich conveys them over an opening in the apparatus, while pieces havingless than said lengths and- [56] References Clted /or widths are allowedto drop through saidopening.

UNlTED STATES PATENTS 3.272.351 9/1966 Burton et a1 271/197 X 8 Claims,7 Drawing Figures Sheet 1 of4 3,918,586

US. Patent Nov. 11, 1975 US. Patent Nov. 11,1975 Sheet2of4 3,918,586

Nov. 11, 1975 Sheet 3 Of4 3,918,586

US. Patent US. Patent Nov. 11, 1975 Sheet4 0f4 3,918,586

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SEPARATING APPARATUS FOR FLAT PIECES OF DIFFERENT DIMENSIONS Thisinvention relates to apparatus for separating desired pieces ofsheet-like material, such as plywood veneers, in accordance withmarginal dimensions. The apparatus can be used for separating undesiredpieces, such as veneer trimmings from the veneers, and/or for separatingthe veneers according to widths thereof.-

Although this apparatus may be used for separating many different formsof sheet-like material, it is primarily designed for separating usableplywood veneers from scraps trimmed therefrom, and for separatingveneers of different widths, and for the sake of convenience, theapparatus will be described for these purposes.

According to standard practice, plywood veneer is cut from the logs in aveneer lathe. This results in the formation of plywood veneers of usablesizes, and others that are not usable. The latter pieces are usually tooshort and/or too narrow. The veneers travel from the lathe with thelength or long dimensions thereof extending across the direction oftravel and so for the sake of convenience the term length as used hereinis the dimension of the veneer across the direction of travel, and theterm width" is the dimension of the veneer in the direction of travel.However, the terms are relative, and therefore this invention is not tobe limited by these terms, but the terms could be interchanged.

As the veneer is moved by conveyor away from the lathe, it passesthrough a clipper where defects, such as knot holes, splits and the likeare cut out. The clipper can be operated manually or automatically. Thedimensions of veneers that are considered usuable differ from mill tomill and with the different wood species being handled. For example, insome plywood plants, pieces that are at least 48 inches long and have aminimum clear width of at least 4 inches are considered to be usuable.The difficulty has been to separate the usable pieces from the scrapmaterial. Furthermore, it is often desirable to separate or classify theusable veneers in accordance with the widths thereof. Up to the presenttime, these two steps have usually been done by hand, and thisnecessitates the use of men who are skilled enough to make a fairjudgement between the usuable and unusable veneers and between thedifferent widths of usable veneers, and who are fast enough to get theusable material off the conveyor. This results in some good veneer beingerroneously left on with undersized pieces to go the scrap conveyor forchipping and/or a poor separation of the usable veneers. In addition,there are times when the men cannot handle all the veneer passing by. Tooffset this, the conveyors have been slowed down to enable the men to doa reasonable job.

Apparatus according to the present invention eliminates or greatlyreduces this problem. As the veneer pieces move away from the clipper onthe conveyor, they pass over sensing means which detect the lengths andwidths thereof. For the sake of convenience, this is called an infeedconveyor, and i the end thereof is spaced from an outfeed conveyor sothat there is a gap or space therebetween. A suitable transportconveyor, such as a suction conveyor, is located above the infeed andoutfeed conveyors and spans the gap therebetween. In this example of theinvention, when the sensor detects an acceptable or desiredveneer'piece, it actuates suitable means which enables the suctionconveyor to take hold of the acceptable piece and transport it to theoutfeed conveyor, upon which the piece is deposited. On the other hand,if the sensing means dete cts an undesired veneer piece under theminimal marginal dimensions, that piece is allowed to reach the end ofthe infeed conveyor, from which it drops through the gap out of theapparatus. The preferred way is to transport the acceptable pieces tothe outfeed conveyor, but it is to be understood that this may bereversed, that is, the scrap may be transported to the outfeed coonveyorand the acceptable pieces allowed to drop through the gap. In the lattercase, there would be receiving means at the gap for conveying theveneers away from the apparatus. If desired, there can be a secondsimilar stage where veneers beyond a certain width are conveyed across agap between two conveyors, while veneers of lesser widths are allowed todrop through this gap.

Although sensing means has been described and illustrated herein for thepresent apparatus, it is to be understood that sensor signals from othersources can be used, such as for example, the sensor signals which causethe standard veneer clipper to operate.

This apparatus eliminates the necessity of using men to remove the scrapmaterial from the conveyor or to separate the good veneers of differentwidths. Not only does this reduce the labour involved, but it is moreaccurate than a man can be, and the conveyors can move at a much fasterspeed than heretofore possible, such as a speed of about 300 feet perminute.

The selection of veneers to be transported across the gap between theinfeed and outfeed conveyors is accomplished by primary suction means,and when this suction means is in operation desired veneers areselected, and when the suction is cut off, veneers are not selected. Inorder to enable this sorting to be accomplished so as to enable theveneers to be fed to the apparatus at high speed, the suction means canbe such that the non-selected veneers are almost instantly repelled orrejected when the suction is cut off.

Apparatus according to this invention comprises an infeed conveyor, anoutfeed conveyor having an end adjacent but spaced from an end of theinfeed conveyor to leave a space therebetween, a transport conveyorabove and extending between the adjacent conveyor ends and having frontand rear ends respectively above the infeed and outfeed conveyor ends,means for applying primary suction to the front end of the transportconveyor to attract pieces from the infeed conveyor to the transportconveyor, means for applying secondary suction to the transport conveyorfrom near the front end thereof to near said rear end, and meansresponsive to dimension sensing means for selectively shutting off andapplying said primary suction to attract or not to attract pieces to thetransport conveyor in accordance with the dimensions of the pieces, saidsecondary suction retaining attracted pieces on the transport conveyorwhile the latter transports said pieces to the outfeed conveyor, andnon-attracted pieces dropping into said gap.

Examples of this invention are illustrated in the accompanying drawings,in which FIG. 1 is a side elevation of the separating apparatus,

FIG. 2 is a plan view of the apparatus,

FIG. 3 is a cross section taken on the line 33 of FIG. 2,

FIG. 4 is a horizontal section taken on the line 44 of FIG. 1,

FIG. 5 is a diagrammatic section illustrating one form of sensor meansas it will be seen on the section line 55 of FIG. 1, 7

FIG. 6 is a sectional view taken on the line .6-6 of FIG. 2, and

FIG. 7 is a diagrammatic side elevation of an alternative form of theapparatus. I

Referring to FIGS. 1 to 6 of the drawings, 10 is a preferred form ofseparating apparatus in accordance with this invention. This apparatusis made up mainly of an infeed conveyor 14 having an end 15 spaced froman end 16 of an outfeed conveyor 18, the spacing of the conveyor endsleaving a gap or space 20 therebetween. This gap is spanned by atransport suction conveyor which overlaps the conveyor ends 15 and 16and is spaced above these ends. When this apparatus is used forseparating plywood veneer pieces, conveyors 14 and 18 are usually wideenough to carry veneers that are more than 8 feet long in the directionacross the conveyor. Although suction conveyor 25 may be the same width,it has been found convenient to place two identical suction conveyors 25side by side, as clearly shown in FIG. 2, in order to attain the desiredwidth. These suction conveyors are coupled together so that they in factconstitute one conveyor, and as these are identical, only one will bedescribed in detail herein..

The infeed and outfeed conveyors may be of any standard design, and inthis example, infeed conveyor 14 is made up of a plurality of laterallyspaced endless belts extending around pulleys 31 at opposite ends of theconveyor, one only of these pulleys being shown in the drawings. Outfeedconveyor 18 is similar to conveyor 14 and is made up of a plurality oflaterally spaced endless belts 34 extending around pulleys 35 atopposite ends of the conveyor, one only -of these pulleys being shown inFIG. 1. These conveyor belts are driven in unison in the usual manner,and the driving means therefore have been omitted.

The suction conveyor 25 includes a plurality of laterally spaced narrowbelts extending around pulleys 42 and 43 mounted respectively on shaft44 and 45 at opposite ends of the conveyor, these shafts beingjournalled in suitable bearings carried by the frame 47 of the conveyor.Shaft 45 has a drive pulley 49 on one end thereof which is operativelyconnected to a suitable source of power, such as an electric motor 50,see FIGS. 1 and 2. The shafts 45 of the two conveyors 25 areinterconnected by a coupling 51, as shown in FIG. 2.

By referring to FIG. 1, it will be seen that pulleys 43 are located overoutfeed conveyor 18 and spaced from the pulleys 35 thereof, whilepulleys 42 lie over infeed conveyor 14 and are spaced from the pulleys31 thereof. The belts 40 are trained over pulleys 53 mounted on shafts54 carried by frame 47 and located immediately above infeed pulleys 31.With this arrangement, the belts 40 have lower runs 55 which areinclined upwardly in a rearward direction and are spaced a little abovethe upper runs of conveyor belts 30 and 34 and overlap the latter belts.

It will be seen from FIGS. 2, 3 and 5 that conveyor belts 40 arearranged in pairs. A suction box is carried by frame 47 and positionedbetween the upper and lower runs of two pairs of these belts which forma conveyor 25. A slot 62 is formed in the bottom of box 60 above thespace between each pair of belts 40, and a pair of tubular members 65and 66 extend along the outer surface of the box bottom at each pair ofbelts.

These tubular members are spaced from each other to leave a slot 67therebetween, said slot registering with the adjacent slot in bottom 63.The lower runs 55 of each pair of the belts 40 travel along the lowersurfaces of members 65 and 66, and if desired wear strips 68 and 69 maybe interposed between said surfaces and the belts. Registering slots 62and 67 bring the interior of suction box 60 into communication with thespace between the adjacent pair of belts 40. By referring to FIG. 1, itwill be seen that the bottom of suction box 60 extends from a front end72 of conveyor 25, which is above gap 20 and near but clear of infeedconveyor end 15, to a rear end 73 of said conveyor, which is locatedover outfeed conveyor 18 and spaced from its end 16. Suction box 60 isconnected by a pipe 74 to a suitable source of suction, such as asuction fan 75.

Sensing means 76 is provided at infeed conveyor 14 to sense the lengthand width of the veneer pieces which are moved by this conveyor towardsgap 20, see FIG. 1. Standard sensor equipment can be used for thispurpose. In this example, the sensing means comprises four banks 78, 79,80 and 81 of photocells, said cells being located on half inch centers,and these banks are located just below the level of the upper runs ofthe belts 30 of infeed conveyors 14 near but spaced away from the end 15of said conveyor. Light sources 84, 85, 86, and 87 are positionedrespectively above banks 78, 79, 80 and 81, see FIG. 5. These sensorsare operatively connected to a suction controller for attracting or notattracting veneer pieces to the front end of conveyors 25. As thissensing and actuating equipment is well known in the art, they do notrequire description herein. For example, this controller may be solenoidmeans for operating a control damper in a suction duct.

The light sources 84 to 87 constantly energize the photo-cells of banks78 to 81. The last cells 88 of the banks are wired as act cells. Thatis, the instant they are covered by a veneer piece and therebyde-energized, the other cells are scanned, and if also covered by a setwidth of material, for example, 6 inches, the control emits an outputsignal. If any two of the banks are covered, indicating that the veneerpiece over the cells is at least 50 inches long, a signal is sent to thecontroller to do the desired job. The banks 78 to 81 may be any lengthand may be spaced apart any desired distances, and in fact, there couldbe one bank extending laterally completely across the infeed conveyor.

Apparatus 10 includes means responsive to the sensing means forattracting selected veneer pieces to transporting or suction conveyor25. The attraction is done by suction means so that when suction isapplied the veneers are attracted to the conveyors 25, and when thesuction is cut off the veneers drop through gap 20. If desired, thesuction can be cut off in such a way as to repel veneers from conveyors25 at the instant of cutoff.

The suction of this suction means is applied only when it is needed, andis termed herein the primary suction, whereas the suction applied by box60 is continuous while the apparatus is in operation, and is called thesecondary suction.

In this example, control suction means 96 is provided for apparatus 10and is located immediately above the end 15 of infeed conveyor 14. Thissuction means includes an elongated chamber 98 extending transversely ofthe apparatus below the upper runs of belt 25 but spacedabove end 15 ofthe infeed conveyor, see FIGS. 1, 2 and This chamber is connected at oneend to the inlet duct 99 of a suction fan 100'which has an outlet ordischarge duct 101. Fan 100 is driven by a motor, not shown. A pluralityof spaced inlet tubes 105 extend downwardly from chamber 98, there beingone of these tubes for each pair of belts 40. By referring to FIG. 3, itwill be seen that each tube 105 opens into chamber 98 at its upper end,and'has an open lower'end 106 which is covered by the tubular members 65and 66 of the adjacent pair of belts 40. The interior of tube 105communicates with slot 67 between these tubular members. In other words,there is a suction tube 105 at the lower runs of each pair of belts 40immediately ahead of suction chamber 60.

The suction of fan 100 is selectively cut off from suction chamber 98 bysuitable damper or'valve means. In this example, a damper 110 is mountedin outlet duct 101 of the fan, and is operable to open and close saidduct. The damper may be operated in any suitable manner, such as bymeans of asolenoid 111. As an alternative to this, a damper 115 may beprovided in inlet duct 99 of the fan, said damper being operated by asolenoid 116. 1

As stated above, it is preferable to provide damper 110 in outlet duct101. This damper is normally open so that fan '100 applies suction tochamber 98 and, consequently, to tubes 105 at the pairs of belts 40.When damper 110 is closed, fan 100 no longer can draw air from chamber98, and as this damper is on the outlet side of the fan, there is aninstant and momentary back pressure through chamber 98, ducts 105 andslots 67.

On theother hand, if damper 115 is used instead of damper 110, whendamper 115 is closed, the suction of fan 100 is cut off from chamber 98and tubes 105. In this example, there is no appreciable back pressurewhen the damper is closed.

With this arrangement, when a piece of veneer having more than theminimum length and width is sensed by the sensor 76, damper 1 10 ordamper 115 is opened to apply suction through slot 67 to the spacesbetween the pairs of belts 40. This suction draws the leading edge ofthe veneer upwardly against the lower runs of conveyor belts 40, and asthese belts are moving across the bottom of suction chamber 60, thesecondary suction in this chamber applied to slots 67 retains the pieceagainst the belts until it clears the rearward end 73 of the chamber, atwhich time the piece drops on to outfeed conveyor 18. Thus, the selectedpiece is attracted to conveyor 25 and conveyed thereby across gap 20 anddeposited on the outfeed conveyor. If the veneer piece moved by infeedconveyor 14 does not have the minimal length and width, the sensor sendsa signal that closes damper 110 or 115 to cut off the suction from thespaces between the pairs of belts 40. This releases the veneer which hasbeen attracted to the conveyor belts to allow it to drop through gap 20.If damper 110 is used, as is preferred, an instant and momentary backpressure is created when the damper is closed, and this repels orrejects the veneer piece very rapidly from the conveyors 25. This backpressure cuts the suction being applied to the veneer instantly. On theother hand, if damper 115 is used in the apparatus, the suction of fan100 is cut off when the damper is closed, but the suction is notinstantaneously cut off from the veneer that has just been attracted tothe transport belt. In other words, the veneer piece does not drop offthe belts as fast as it does when damper 110 is employed. As a result,infeed conveyor has to be operated at a slower speed then when damper110 is used. The big advantage'of the latter'damper is that itsimultaneously cuts off th suction and applies'the back undersizedveneer piece.

Although apparatus can be. used for sorting or classifying veneersof'different widths, it is primarily intended for separating goodveneers from scrap veneer following the action ofa veneer clipper. Inactual practice, the signals that cause the clipper to operate can beused to control suction means 96 of the apparatus.

FIG. 7 illustrates apparatus that can be used to separate veneers fromtrimmings, and to separate good veneers of different widths. Thisembodiment includes apparatus 10 with its infeed belt 14 and outfeedbelt 18, and a similar. apparatus 10a in which conveyor 18 acts as theinfeed conveyor, and. another similar conveyor pressure to repel the-125 acts as the outfeed conveyor therefor.

Apparatus 10a functions in the same manner as apparatus 10. If sensor76'detects a veneer of a width beyond a predetermined width, it signalsto apparatus 10a to cause the primary suction thereof to attract thepiece to transport belts 40 so that. it is carried over gap 20a anddeposited on to conveyor 125. If the sensor detects a piece having asmaller width but wider than the predetermined minimal width, theprimarysuction is cut offand the piece is allowed to drop through gap20a. It is usually desirable to provide a receiver 130 at this gap so asto receive these pieces.

It is obvious that the apparatus may have as many units 10 in successionin order to accomplish adesired degree of classification of .the veneerpieces.

, As pointed out above, an important feature of this invention is theuse of damper in the outlet duct of the primary suction fan. This, whenclosed, creates the almost instant back pressure which rapidly separatesthe non-selected piece from the transport belts. Efforts have been madein the past to use suction to attract sheet material to belt conveyorsand to release the sheets by cutting off the suction and applyingpressure in an attempt to accomplish this action in a rapid manner.However, the known apparatus requires two separate systems, the suctionsystem and a pressure system, and this requires space and comparativelycostly elements in the two systems. In addition, when attempts are madeto cut off suction and apply pressure, there is also difficulty ofbalancing these correctly, and even when they are correctly balanced,they are relatively slow since it takes time to move pressure valvesrelative to suction valves.

We claim:

1. Apparatus for separating pieces of sheet-like material having atleast predetermined marginal dimensions from other pieces of less thanthe predetermined marginal dimensions, said apparatus being adapted tobe used in association with sensing means which is operable to sense thedimensions of pieces being directed to the apparatus, said apparatuscomprising an infeed convenor, an outfeed conveyor having an endadjacent but spaced from an end of the infeed conveyor to leave a gaptherebetween, a transport conveyor above and extending between theadjacent conveyor ends and having from and rear ends respectivelyoverlapping and above the infeed and outfeed conveyor ends, means forapplying primary suction to the front end of the transport conveyor overthe infeed conveyor to attract pieces from the infeed conveyor to thetransport conveyor, means for applying secondary suction to thetransport conveyor from near the front end thereof to near said rear endand over said adjacent end of the outfeed conveyor, and means responsiveto said sensing means for selectively shutting off and applying saidprimary suction to attract or not to attract pieces to the transportconveyor in accordance with the dimensions of the pieces, said secondarysuction retaining attracted pieces on the transport conveyor while thelatter transports said pieces to the outfeed conveyor, and nonattractedpieces dropping into said gap.

2. Apparatus as claimed in claim 1 in which said means for applyingprimary suction comprises a suction fan having an inlet duct and anoutlet duct, and said means for shutting off and applying said primarysuction comprises a damper in said outlet duct, whereby the closing ofsaid damper in the duct cuts off the primary suction and simultaneouslycreates an instant and momentary back pressure to repel pieces from thetransport conveyor.

3. Apparatus as claimed in claim 1 in which said means for applyingprimary suction comprises a suction fan having an inlet duct and anoutlet duct, and said means for shutting off and applying said primarysuction comprises a damper in said inlet duct, whereby the closing ofsaid damper cuts off the primary suction to allow pieces to fall awayfrom the transport conveyor.

4. Separating apparatus as claimed in claim 1 wherein said sensing meanscomprises a plurality of photo electric cells across and below andextending longitudinally of the infeed conveyor, and light means abovesaid conveyor and directed on to said cells.

5. Separating apparatus as claimed in claim 1 wherein said transportconveyor comprises a plurality of parallel laterally spaced endlessbelts, and said secondary suction means extends longitudinally along atleast some of the belts and is positioned to suck attracted piecesagainst said belts to be moved thereby.

6. Separating apparatus as claimed in claim 1 wherein said transportconveyor comprises a plurality of parallel laterally spaced endlessbelts, said belts being arranged in closely spaced pairs to form narrowspaces therebetween, and said secondary suction means comprises a closedsuction box having slots therein opening into the narrow spaces betweenportions of pairs of belts against which the pieces bear while beingtransported by said belts.

7. Apparatus as claimed in claim 6 in which said means for applyingprimary suction comprises a suction fan having an inlet duct and anoutlet duct, said inlet duct being in communication only with saidnarrow spaces between said pairs of belts, and said means for shuttingoff and applying said primary suction comprises a damper in said outletduct, whereby the closing of said damperin the duct cuts off the primarysuction from the narrow spaces between the pairs of belts andsimultaneously creates an instant and momentary backpressure in saidspaces to repel pieces from the transport conveyor.

8. Apparatus as claimed in claim 6 in which said means for applyingprimary suction comprises a suction fan having an inlet duct and anoutlet duct, and said means for shutting off and applying said primarysuction comprises a damper in said inlet duct, whereby the closing ofsaid damper cuts off the primary suction to allow pieces to fall awayfrom the transport conveyor.

1. Apparatus for separating pieces of sheet-like material having atleast predetermined marginal dimensions from other pieces of less thanthe predetermined marginal dimensions, said apparatus being adapted tobe used in association with sensing means which is operable to sense thedimensions of pieces being directed to the apparatus, said apparatuscomprising an infeed convenor, an outfeed conveyor having an endadjacent but spaced from an end of the infeed conveyor to leave a gaptherebetween, a transport conveyor above and extending between theadjacent conveyor ends and having front and rear ends respectivelyoverlapping and above the infeed and outfeed conveyor ends, means forapplying primary suction to the front end of the transport conveyor overthe infeed conveyor to attract pieces from the infeed conveyor to thetransport conveyor, means for applying secondary suction to thetransport conveyor from near the front end thereof to near said rear endand over said adjacent end of the outfeed conveyor, and means responsiveto said sensing means for selectively shutting off and applying saidprimary suction to attract or not to attract pieces to the transportconveyor in accordance with the dimensions of the pieces, said secondarysuction retaining attracted pieces on the transport conveyor while thelatter transports said pieces to the outfeed conveyor, and non-attractedpieces dropping into said gap.
 2. Apparatus as claimed in claim 1 inwhich said means for applying primary suction comprises a suction fanhaving an inlet duct and an outlet duct, and said means for shutting offand applying said primary suction comprises a damper in said outletduct, whereby the closing of said damper in the duct cuts off theprimary suction and simultaneously creates an instant and momentary backpressure to repel pieces from the transport conveyor.
 3. Apparatus asclaimed in claim 1 in which said means for applying primary suctioncomprises a suction fan having an inlet duct and an outlet duct, andsaid means for shutting off and applying said primary suction comprisesa damper in said inlet duct, whereby the closing of said damper cuts offthe primary suction to allow pieces to fall away from the transportconveyor.
 4. Separating apparatus as claimed in claim 1 wherein saidsensing means comprises a plurality of photo electric cells across andbelow and extending longitudinally of the infeed conveyor, and lightmeans above said conveyor and directed on to said cells.
 5. Separatingapparatus as claimed in claim 1 wherein said transport conveyorcomprises a plurality of parallel laterally spaced endless belts, andsaid secondary suction means extends longitUdinally along at least someof the belts and is positioned to suck attracted pieces against saidbelts to be moved thereby.
 6. Separating apparatus as claimed in claim 1wherein said transport conveyor comprises a plurality of parallellaterally spaced endless belts, said belts being arranged in closelyspaced pairs to form narrow spaces therebetween, and said secondarysuction means comprises a closed suction box having slots thereinopening into the narrow spaces between portions of pairs of beltsagainst which the pieces bear while being transported by said belts. 7.Apparatus as claimed in claim 6 in which said means for applying primarysuction comprises a suction fan having an inlet duct and an outlet duct,said inlet duct being in communication only with said narrow spacesbetween said pairs of belts, and said means for shutting off andapplying said primary suction comprises a damper in said outlet duct,whereby the closing of said damper in the duct cuts off the primarysuction from the narrow spaces between the pairs of belts andsimultaneously creates an instant and momentary back pressure in saidspaces to repel pieces from the transport conveyor.
 8. Apparatus asclaimed in claim 6 in which said means for applying primary suctioncomprises a suction fan having an inlet duct and an outlet duct, andsaid means for shutting off and applying said primary suction comprisesa damper in said inlet duct, whereby the closing of said damper cuts offthe primary suction to allow pieces to fall away from the transportconveyor.